U.S. patent application number 14/127259 was filed with the patent office on 2014-05-15 for valve actuation mechanism and automotive vehicle comprising such a valve actuation mechanism.
This patent application is currently assigned to RENAULT TRUCKS. The applicant listed for this patent is Romain Le Forestier, Romain Riviere. Invention is credited to Romain Le Forestier, Romain Riviere.
Application Number | 20140130774 14/127259 |
Document ID | / |
Family ID | 44906231 |
Filed Date | 2014-05-15 |
United States Patent
Application |
20140130774 |
Kind Code |
A1 |
Le Forestier; Romain ; et
al. |
May 15, 2014 |
VALVE ACTUATION MECHANISM AND AUTOMOTIVE VEHICLE COMPRISING SUCH A
VALVE ACTUATION MECHANISM
Abstract
A valve actuation mechanism includes rockers moved by a
camshaft, each rocker being adapted to exert a valve opening force
on at least a portion of a valve opening actuator of each cylinder,
via an activation piston, housed in a bore of the rocker and
movable with respect to the rocker under action of a fluid pressure
raise in a chamber fluidly linked to the bore, from a first
position to a second position, in which a cam follower of the
rocker reads at least one auxiliary cam sector of a cam of the
camshaft so as to perform an engine operating function. Each rocker
includes a reset valve adapted to reduce fluid pressure in the
chamber. The valve actuation mechanism includes, for each rocker, a
reset cam profile adapted to open the reset valve when the
activation piston has to be moved from its second position to its
first position, and each reset valve includes a cam follower
adapted to drive the reset valve as a function of the movement of
the reset profile.
Inventors: |
Le Forestier; Romain;
(Reyrieux, FR) ; Riviere; Romain; (Pollionnay,
FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Le Forestier; Romain
Riviere; Romain |
Reyrieux
Pollionnay |
|
FR
FR |
|
|
Assignee: |
RENAULT TRUCKS
Saint Priest
FR
|
Family ID: |
44906231 |
Appl. No.: |
14/127259 |
Filed: |
July 6, 2011 |
PCT Filed: |
July 6, 2011 |
PCT NO: |
PCT/IB2011/002189 |
371 Date: |
December 18, 2013 |
Current U.S.
Class: |
123/321 ;
123/90.44 |
Current CPC
Class: |
F02D 9/06 20130101; F01L
13/08 20130101; F01L 1/181 20130101; F01L 13/06 20130101; F01L
1/2416 20130101; F01L 13/0021 20130101 |
Class at
Publication: |
123/321 ;
123/90.44 |
International
Class: |
F01L 13/06 20060101
F01L013/06; F01L 1/24 20060101 F01L001/24; F02D 9/06 20060101
F02D009/06 |
Claims
1. Valve actuation mechanism for an internal combustion engine on
an automotive vehicle, comprising rockers moved by a camshaft, each
rocker being adapted to exert a valve opening force on at least a
portion of a valve opening actuator of each cylinder, via an
activation piston of the rocker and movable with respect to the
rocker under action of a fluid pressure raise in a chamber, from a
first position, to a second position, in which a cam follower of
the rocker reads at least one auxiliary valve lift sector of a cam
of the camshaft so as to perform an engine operating function, each
rocker comprising a reset valve, adapted to release fluid from the
chamber, wherein the valve actuation mechanism comprises, for each
rocker, a reset cam profile adapted to open the reset valve when
the activation piston has to be moved from its second position to
its first position, and wherein each rocker comprises a cam
follower, adapted to drive the reset valve as a function of the
movement of the reset profile.
2. Valve actuation mechanism according to claim 1, wherein the
reset profile is made on a reset cam of a camshaft of the valve
actuation mechanism, and wherein the cam follower of the reset
valve cooperates with the reset cam.
3. Valve actuation mechanism according to claim 2, wherein the
reset cam is integral with or mounted on the camshaft which moves
the rocker on which the reset valve is mounted.
4. Valve actuation mechanism according to claim 1, wherein the
reset profile is made on the cam follower of the reset valve, and
wherein the reset profile cooperates with the cam which is read by
the cam follower of the rocker.
5. Valve actuation mechanism according to claim 1, wherein the cam
follower of the reset valve comprises a lever arm.
6. Valve actuation mechanism according to claim 5, wherein the
reset valve is rotatable around a longitudinal axis, and wherein
the lever arm is fast in rotation with the reset valve.
7. Valve actuation mechanism according to claim 6, wherein the
lever arm is mounted on a shaft of the reset valve, the shaft
protruding outside the rocker along a rotation axis of the reset
valve.
8. Valve actuation mechanism according to claim 1, wherein each
rocker comprises a check valve movable between a first position, in
which the check valve allows passage of fluid between the chamber
and a fluid circuit feeding the chamber, and a second position, in
which the check valve blocks passage of fluid between the chamber
and the fluid circuit and wherein each reset valve is adapted to
bypass the check valve and link the chamber and the fluid circuit
feeding the chamber.
9. Valve actuation mechanism according to claim 8, wherein the
reset valve comprises two parallel through holes and two parallel
grooves linking the through holes with each other, and wherein the
through holes communicate with the duct which bypasses the check
valve when the reset valve is in its opened position.
10. Valve actuation mechanism according to claim 8, wherein the
reset valve comprises a peripheral surface adapted to obturate the
duct which bypasses the check valve when the reset valve is in its
closed position.
11. Valve actuation mechanism according to claim 10, wherein the
reset valve has a cylindrical form with a circular section.
12. Valve actuation mechanism according to claim 1, wherein it is
an exhaust valve actuation mechanism.
13. Valve actuation mechanism according to claim 12, wherein the
activation piston activates an exhaust gas recirculation function
when it is in its second position.
14. Valve actuation mechanism according to claim 12, wherein the
activation piston activates an engine brake function when it is in
its second position.
15. Valve actuation mechanism according to claim 14, wherein the
engine brake function is realized by opening two exhaust valves and
wherein the valve opening force is exerted by the activation piston
on the whole valve opening actuator.
16. Valve actuation mechanism according to claim 14, wherein the
engine brake function is realized by opening one of two exhaust
valves, wherein the portion of the valve opening actuator on which
the valve opening force is exerted is slider block, on which the
valve is mounted and which is movable, with respect to the valve
opening actuator, along the opening axis of the valve, and wherein
each rocker comprises a finger adapted to exert, under rotation of
the rocker, a valve opening force on the remaining portion of the
valve opening actuator, on which the second valve (5) is
mounted.
17. Valve actuation mechanism according to claim 1, wherein it is
an intake valve actuation mechanism.
18. An automotive vehicle comprising a valve actuation mechanism
according to claim 1.
Description
BACKGROUND AND SUMMARY
[0001] The invention concerns a valve actuation mechanism for an
internal combustion engine on an automotive vehicle. The invention
also concerns an automotive vehicle, such as a truck, equipped with
such a valve actuation mechanism.
[0002] Automotive vehicles, such as trucks, often rely on an engine
brake function to slow down in order, for example, to reduce wear
of the friction brake pads and to prevent overheating of the
friction brakes, particularly on downward slopes. It is known to
perform engine brake by acting on the amount of gas present in the
cylinders of the engine in two distinct phases. In a first phase,
when the pistons are near a bottom dead center, one injects exhaust
gases into the chambers of the cylinders so as to slow down the
pistons when they move towards their high level. This is done by
slightly opening at least a valve connected to an exhaust manifold,
while exhaust gases are prevented to be expelled from the exhaust
pipe and thereby at a certain pressure above atmospheric pressure.
In the second phase, the gases which are compressed by the piston
are expelled from the chamber of the cylinder when the piston is at
or near its top dead center position in order to prevent an
acceleration of the piston under effect of volcanic expansion of
compressed gas. This is done by slightly opening a valve so as to
expel gases from the cylinder. In most cases, the valve (or valves)
which is (are) opened for the engine brake function is (are) a main
exhaust valve. An engine brake system is described in document
9009514.
[0003] To perform these engine brake valves movements, also called
engine brake valves lifts, the engine comprises, for each cylinder,
a rocker acting, on the valves to open and close them. The rocker
is acted upon by a rotating cam which has at least one lift sector
to cause the lifting (opening) of the valve. If the valve is also
an exhaust or an intake valve, the corresponding cam will comprise
a main valve lift sector and one or several auxiliary valve lift
sectors (also called main valve lift bump and auxiliary valve lift
bump) When engine brake is needed, a cam follower surface of the
rocker is moved in close contact with a cam of a camshaft moving
the rocker so that the brake movements of the valve are obtained,
when the cam follower interacts with the auxiliary valve lift
sectors. In normal operating conditions of the engine, the valves
should not perform these movements and the roller of the rocker is
kept slightly remote from the cam so that the cam follower does not
interact with the auxiliary valve lift sectors. The distance or
clearance between the roller and the cam ensures that only the
larger main lift sector on the cam, dedicated to the main exhaust
event, causes an opening of the exhaust valve, but not one or
several smaller auxiliary lift sectors dedicated to the engine
brake function. This clearance is suppressed when engine brake is
needed, by moving an activation piston of the rocker to make a
close contact between the roller and the cam, so that engine brake
dedicated lift sectors on the cam also cause an opening of the
valve. An engine brake system having such valve actuation mechanism
is described in WO-91/08381
[0004] In the case of a system where two valves are to be actuated,
the piston can be in contact with the valves through a valve
bridge.
[0005] When the engine brake valve opening(s) have been performed,
a reset function is preferably to be performed. In other words, the
activation piston needs to be moved towards its initial position in
order to ensure that the valves are closed early enough before fuel
admission, in order to prevent negative airflow by valve
overlapping.
[0006] Engine brake systems generally comprise a control valve to
direct pressurized control fluid pressure in a chamber adjacent to
the piston to move the activation piston from its initial position
to its engine brake actuation position. The control valve controls
whether or not the engine brake function is activated. This control
valve lets pressurized control fluid flow, at a pressure of for
example 2 to 5 bars, towards each rocker as long as the engine
brake function is needed. which typically lasts several seconds or
tens of seconds during which the engine and the cam shaft may
perform several hundreds or thousands of complete revolutions. In
some systems, a check valve is provided to prevent any fluid flow
out of the chamber. In some known systems, such as the one
described in WO-91/08381, the check valve can nevertheless be
forced to an open position, allowing the control fluid to escape
the chamber when the engine brake is not needed. This is achieved
when no control pressure is sent to the control valve. In known
systems, there is only one control valve for several cylinders, so
that it is not possible to use the control valve to empty the
chamber to allow retraction of the piston, if such retraction is
needed for a period of time inferior to one revolution of the
camshaft.
[0007] It is known from U.S. Pat. No. 5,890,469 to use a rotating
by-pass valve, housed inside the rocker and which opens or closes a
fluid circuit in which a pressure raise provokes the outward
movement of the piston. This by-pass valve is opened when the
piston must be pushed back. The by-pass valve is rotated by a gear
fixed to the rotation axis of the rocker. The solution of U.S. Pat.
No. 5,890,469 is not entirely satisfying because, when a single
valve engine brake technology is used, the reset valve opens the
fluid circuit but at a time when no force is exerted on the piston
to push it back in its normal position so that it tends to stay in
a second position. At the time the valve springs exert a force on
the piston, the fluid circuit is not opened, tending to prevent the
piston from moving back to its first position.
[0008] It is desirable to provide a valve actuation mechanism in
which, when a specific operation of the engine must he activated,
the piston can be reset to its first position by using the by-pass
valve especially with a single valve brake technology.
[0009] To this end, an aspect of the invention concerns a valve
actuation mechanism for an internal combustion engine on an
automotive vehicle, comprising rockers moved by a camshaft, each
rocker being adapted to exert a valve opening force on at least a
portion of a valve opening actuator of each cylinder, via an
activation piston of the rocker, movable with respect to the rocker
under action of a fluid pressure raise in a chamber, from a first
position, to a second position, in which a cam follower of the
rocker reads at least one auxiliary valve lift sector of a cam of
the camshaft so as to perform an engine operating function, each
rocker comprising a reset valve, adapted to release fluid pressure
in the chamber. The valve actuation mechanism is characterized in
that it comprises, for each rocker, a reset cam profile adapted to
open the reset valve when the brake activation piston has to be
moved from its second position to its first position, and in that
each reset valve comprises a cam follower, adapted to drive the
reset valve as a function of the movement of the reset profile.
[0010] Thanks to an aspect of the invention, the movement of the
reset valve is not only dependant on the movements of the rocker
and can be controlled by the movements of the reset cam or of the
cam follower. This permits to open the reset valve exactly when
needed and independently for each rocker. The fluid circuit is
opened and the pressure reduced at the moment when the force of the
springs which maintain the valves in their closed position is
exerted on the activation piston. This permits to reduce the valve
overlapping between the intake and the exhaust valves.
[0011] According to further aspects of the invention which are
advantageous but not compulsory, such a valve actuation mechanism
may incorporate one or several of the following features: [0012]
The reset profile is made on a reset cam of a camshaft of the valve
actuation mechanism, and whereas the cam follower of the reset
valve cooperates with the reset cam. [0013] The reset cam is
integral with or mounted on the camshaft which moves the rocker on
which the reset cam is mounted. [0014] The reset profile is made on
the cam follower of the reset valve, and whereas the reset profile
cooperates with the cam which is read by the cam follower of the
rocker. [0015] The cam follower of the reset valve comprises a
lever arm. [0016] The reset valve is rotatable around a
longitudinal axis, and whereas the lever arm is fast in rotation
with the reset valve. [0017] The lever are is mounted on a shaft of
the reset valve, said shaft protruding outside the rocker along a
rotation axis of the reset valve. [0018] Each rocker comprises a
check valve movable between a first position, in which the check
valve allows passage of fluid between the chamber and a fluid
circuit feeding the chamber, and a second position, in which the
check valve blocks passage of fluid between the chamber and the
fluid circuit and whereas each reset valve is adapted to bypass the
check valve and links the chamber and the fluid circuit feeding the
chamber. [0019] The reset valve comprises two parallel through
holes and two parallel grooves linking the through holes with each
other, and whereas the through holes communicate with the duct
which bypasses the check valve when the reset valve is in its
opened position. [0020] The reset valve comprises a peripheral
surface adapted to obturate the duct which bypasses the check valve
when the reset valve is in its closed position. [0021] The reset
valve has a cylindrical form with a circular section. [0022] The
valve mechanism is an exhaust valve actuation mechanism. [0023] The
activation piston activates an exhaust gas recirculation function
when it is in its second position. [0024] The activation piston
activates an engine brake function when it is in its second
position. [0025] The engine brake function is realized by opening
two exhaust valves and whereas the valve opening force is exerted
by the activation piston on the whole valve opening actuator.
[0026] The engine brake function is realized by opening one of two
exhaust valves, whereas the portion of the valve opening actuator
on which the valve opening force is exerted is a slider block, on
which said valve is mounted and which is movable, with respect to
the valve opening actuator, along the opening axis of said valve,
and whereas each rocker comprises a finger adapted to exert, under
rotation of the rocker, a valve opening force on the remaining
portion of the valve opening actuator, on which the second valve is
mounted. [0027] The valve actuation mechanism is an intake valve
actuation mechanism.
[0028] The invention also concerns an automotive vehicle, such as a
truck, comprising a valve actuation mechanism as mentioned here
above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] The invention will now be explained in correspondence with
the annexed figures, as illustrative example. In the annexed
figures:
[0030] FIG. 1 is a perspective view of a valve actuation mechanism
according to a first embodiment of the invention;
[0031] FIG. 2 is a perspective view of a reset valve belonging to
the valve actuation mechanism of FIG. 1;
[0032] FIG. 3 is a sectional view along plane III on FIG. 1, of a
rocker belonging to the valve actuation mechanism of FIG. 1, in a
first configuration;
[0033] FIG. 4 is a sectional view, along line IV on FIG. 3 of the
rocker of FIG. 3;
[0034] FIG. 5 is a sectional view similar to FIG. 3, for a second
configuration of the rocker;
[0035] FIG. 6 is a sectional view similar to FIG. 4, for the second
configuration of the rocker;
[0036] FIG. 7 is a perspective view similar to figure of a valve
actuation mechanism according to a second embodiment of the
invention.
[0037] FIG. 8 is a perspective view similar to FIG. 1, of a valve
actuation mechanism according to a third embodiment of the
invention.
DETAILED DESCRIPTION
[0038] The valve actuation mechanism S represented on FIG. 1
comprises a camshaft 2 rotatable around a longitudinal axis X2.
Camshaft 2 comprises several cams 22, each being dedicated to
moving the valves of one cylinder of an internal combustion engine
E of a non-represented automotive vehicle on which valve actuation
mechanism S is integrated. Each cam has a cam profile which may
comprise one or several "bumps", i.e. valve lift sectors where the
cam profile exhibits a bigger eccentricity with respect to axis X2
than the base radius of the cam.
[0039] In this embodiment, each cylinder of engine E is equipped
with two exhaust valves 4 and 5. Valves 4 and 5 are kept in a
closed position by respective springs 41 and 51. Each valve 4 and 5
is movable in translation along an opening axis X4 or X5 so as to
be opened, or lifted. More precisely, translation of valves 4 and 5
opens a passageway between the combustion chamber of the cylinder
and an exhaust manifold. Valves 4 and 5 are connected to a valve
bridge 7, which forms a valve opening actuator, and which extends
substantially perpendicularly to axes X4 and X5. in case only one
valve is to be actuated, then the opening actuator can be integral
with the valve, for example embodied as a top portion of the valve
stem.
[0040] Valves 4 and 5 are partly represented on FIGS. 1 and 2, only
their respective stems are visible.
[0041] For each cylinder, the transmission of movement between
camshaft 2 and valve bridge 7 is performed by a rocker 9 rotatable
with respect to a rocker shaft 91 defining a rocker rotation axis
X91. Only one rocker 9 is represented on the figures. Each rocker 9
comprises a roller 93 which acts as a cam follower and cooperates
with a cam 22. Roller 93 is located on one side of rocker 9 which
respect to shaft 91. Each rocker 9 comprises, opposite to roller 93
with respect to shaft 91, an activation piston 95 adapted to exert
a valve opening force F9 on the whole of valve bridge 7.
Particularly, rotation of camshaft 2 transmits, when the roller
runs a valve lift sector of the cam, a rotation movement R1 to
rocker 9 via roller 93, this rotation movement inducing a
translation movement of valve bridge 7 along an axis X7 which is
parallel to axes X4 and X5.
[0042] Cooperation between a main valve lift sector 220 of cam 22
and roller 93, on the one hand, and between piston 95 and bridge 7,
on the other hand, generates exhaust openings of valves 4 and 5
during the corresponding operating phase of internal combustion
engine E.
[0043] In the shown embodiment, rocker shaft 91 is hollow and
defines a duct 911 which houses a control fluid circuit connected
to a non-shown fluid tank of valve actuation mechanism S. Rocker 9
comprises a non represented internal fluid circuit which fluidly
connects duct 911 to a piston chamber 101 of rocker 9, delimited by
piston 95, via a check valve 97. Piston 95 is housed in to bore 94
of rocker 9 and adapted to move with respect to chamber 101 along a
translation axis X95 corresponding to a longitudinal axis of piston
95.
[0044] Cam 22 comprises at least one, but here two auxiliary valve
lift sectors 221 and 222 which are adapted to cooperate with roller
93. These sectors induce, when read by roller 93 of rocker 9, two
additional pivoting movements of rocker 9 on each turn of camshaft
2. The auxiliary lift sectors 221 and 222 are usually designed to
cause only a limited lift of the valve, as they are not intended to
allow a great flow of gases through the valve. These two pivoting
movements are transformed by piston 95 into two opening movements
of valves 4 and 5 so as to perform an engine brake function at two
precise moments during operation of engine E, as described briefly
above. The purpose and effects of these valve openings are
well-known and will not be further described hereafter. According
to an alternate embodiment, cam 22 comprises only one auxiliary
valve lift sector for performing only one opening of valves 4 and 5
on each turn of camshaft 2, in addition to the main exhaust valve
opening.
[0045] When engine F switches to engine brake mode, check valve 97
is opened so that fluid can flow from duct 911 to the inside of
rocker 9 and subsequently to piston chamber 101 so as to induce a
pressure raise in piston chamber 101. The pressure raise in chamber
101 induces translation movement of piston 95 outwardly with
respect to rocker 9, from a first position, in which piston 95 is
entirely or partially pushed back into chamber 101, to a second
position, in which piston 95 is partially moved out of piston
chamber 101 until it comes in abutment against valve bridge 7.
Preferably, the control fluid is a substantially incompressible
fluid such as oil.
[0046] When piston 95 is in its first position, retracted, as shown
on FIG. 2, roller 93 is offset with respect to the auxiliary valve
lift sectors 221 and 222 of cam 22 by an engine brake actuation
clearance, so that when camshaft 2 rotates around axis X2, cam 22
does not come in contact with roller 93, or piston 95 does not come
in contact with valve bridge 7. By moving piston 95 to its second
position, extended, as shown on FIG. 4, rocker 9 pivots around the
longitudinal axis X91 of shaft 91, in the direction of arrow A1.
Thus, the actuation clearance is suppressed and roller 93 comes
into contact with the auxiliary valve lift sectors of cam 22,
allowing engine brake operations to be implemented.
[0047] According to a variant of the invention, piston 95 may be
adapted to activate or deactivate an internal exhaust gases
recirculation function. This function allows an exhaust valve
opening during the intake stroke. By returning a controlled amount
of exhaust gas to the combustion process, peak combustion
temperatures are lowered. This will reduce the formation of
Nitrogen oxides (NOx).
[0048] The fluid circuit housed inside rocker 9 comprises a main
duct 103 which fluidly links check-valve 97 with piston chamber
101. Main duct 103 opens on the outside of rocker 9 and fluid is
prevented from going out of rocker 9 by a shutter element 105
screwed into a threaded portion of main duct 103. A seat element
107 is press-fitted into main duct 103. A ball 109 of check-valve
97 is adapted to cooperate with seat element 107 so as to block
passage of fluid from piston chamber 101 back to duct 911. Ball 109
is biased towards seat element 107 by a spring 111 and therefore
tends to close the check-valve 97. When no control pressure comes
from duct 91, ball 109 is kept in open position by a plunger 110
spring-biased by a spring 112 arranged in chamber 113, the action
of the spring 112 being superior to the action of spring 111.
[0049] On the other side of check-valve 97 with respect to main
duct 103, rocker 9 comprises a fluid inlet chamber 113. Fluid
coming from duct 911 first flows into fluid inlet chamber 113. An
upstream by-pass duct 115 originates from fluid inlet chamber 113
and comes to a by-pass chamber 117. A downstream by-pass duct 119
fluidly connects bypass chamber 117 to main duct 103. In other
words, upstream by-pass duct 115, by-pass chamber 117 and
downstream by-pass duct 119 define together a by-pass passage of
check-valve 97.
[0050] By-pass chamber 117 has a cylindrical form with circular
section. Each of ducts 115 and 119 opens into by-pass chamber 117
in the vicinity of one of its planar inner walls.
[0051] Rocker 9 further comprises a reset valve 99. The reset valve
has the function of allowing control fluid to escape from chamber
101 to allow retraction of the activation piston to its first
position.
[0052] In the shown embodiment, the reset valve is a distinct
valve. It is housed inside bypass chamber 117 and adapted to
rotate, around a longitudinal axis X99 of reset valve 99, which
corresponds to a longitudinal axis of by-pass chamber 117. Reset
valve 99 has a cylindrical form with circular section corresponding
to the form of by-pass chamber 117.
[0053] Reset valve 99 comprises a first through hole 991, which is
perpendicular to axis X99 and opens on opposite zones of the
peripheral surface of reset valve 99. In mounted configuration of
reset valve 99 in by-pass chamber 117, through hole 991 and
upstream by-pass duct 115 are in a same plane perpendicular to axis
X99. Reset valve 99 further comprises a second through hole 993
similar to through hole 991 located at the other end of reset valve
993. Through hole 993 and downstream by-pass duct 119 are in a same
plane perpendicular to axis X99 in mounted configuration of reset
valve 99.
[0054] Reset valve 99 further comprises two parallel grooves 995,
which are realized parallel to axis X99 on the peripheral surface
of reset valve 99. Grooves 995 communicate with through holes 991
and 993. Longitudinal axes of grooves 995 and holes 991 and 993
define a plane containing a diameter of reset valve 99 and axis
X99.
[0055] On its end located in the vicinity of through hole 991,
reset valve 99 comprises a shaft 997 which protrudes outside rocker
9 along axis X99. A lever arm 13 is fixed to shaft 997. Lever arm
13 extends perpendicularly to the axis of the reset valve. In this
embodiment, it is drop-shaped and has a thin end on the side of
shaft 997, and a circular shaped end comprising a circular rolling
surface 131, the axis of which is remote and parallel to axis X99.
According to a non-shown alternate embodiment, an intermediate
transmission mechanism may transmit the rotation of lever arm 13 to
reset valve 99. Camshaft 2 comprises, offset with respect to cam 22
along axis X2, a reset cam 26 having a reset profile which is
aligned with rolling surface 131 of lever arm 13, which forms a cam
follower. Thus, rotation of camshaft 2 induces, via reset cam 26,
the transmission of a rotation movement to lever arm 13 around axis
X99.
[0056] According to a non-shown alternate embodiment, an
intermediate transmission mechanism may transmit the rotation
movement from reset cam 26 to lever arm 13.
[0057] According to an alternate non-shown embodiment, reset cam 26
may be carried by another shaft of valve actuation mechanism S,
independent from camshaft 2.
[0058] In the shown example, the reset cam is a rotating cam, but
it could be a cam having a different movement, for example an
alternate back and forth translation movement synchronized with the
rotation of cam 22.
[0059] In other words, the rocker 9 comprises a cam follower which
is associated to the reset valve is such a way that the cam
follower, when cooperating with the reset profile of reset cam,
controls the opening or the closing of the reset valve. The cam
follower can be integral with the reset valve, as in the embodiment
shown on the figures, or distinct therefrom. The cam follower is
preferably carried by the rocker.
[0060] In any case, the reset profile and the reset cam follower
are adapted to create a relative movement of the reset valve 99
with respect to the corresponding rocker. This relative movement is
nevertheless coordinated with the movement of the rocker with
respect to the engine housing so that the reset function is
performed at a selected given time within the opening/closing cycle
of the valves 4 and 5.
[0061] In this embodiment, rotation of lever arm 13 around axis X99
under action of reset cam 26 induces a rotation of reset valve 99
relative to the corresponding rocker between a closed position and
an opened position. In its closed position, reset valve 99 is
positioned with respect to by-pass chamber 117 so that upstream
by-pass duct 115 and downstream by-pass duct 119 are not aligned
with through holes 991 and 993. Upstream bypass duct 115 and
downstream bypass duct 119 are obturated by peripheral cylindrical
surface 990 of reset valve 99. In this case, fluid can not by-pass
check valve 97. In opened position of reset valve 99, through holes
991 and 993 are respectively aligned with upstream by-pass duct 115
and downstream by-pass duct 119. Fluid can therefore flow in
grooves 995 and check valve 97 is by-passed.
[0062] The invention operates in the following way: before
activation of the engine brake function, check valve 97 is in
opened position, due to action of the spring biased plunger 110.
When the engine brake function is activated, the control valve
sends pressurized oil in duct 911. This pressure arrives in 113
below the plunger and forces retraction of the plunger which does
not anymore force the check valve to its open position, so that it
now functions as a normal check-valve. As long a pressure in
chamber 101 is lower than control pressure (3 bars), the control
pressure fills chamber 101. Indeed, the spring 111 which biases the
ball 109 towards the seat element has a low spring rate and allows
opening of the check-valve if pressure on the duct side of the ball
109 is only slightly superior to the pressure on the chamber side
of the ball 109, for example by a margin of 0.5 bars. Fluid may
then flow through check-valve 97 into piston chamber 101 until
pressure raise is sufficient to move piston 95 to its second
position. To the contrary, when, due to an external effort on
piston 95, fluid in chamber 101 tends to flow backwards towards
duct 911, then the check valves closes, preventing such a
back-flow. Indeed pressure downstream of ball 109 becomes higher
than pressure upstream of ball 109, check valve 97 then closes
itself, preventing piston 95 from returning to its first position.
Translation of piston 95 induces a rotation of rocker 9 around axis
X91, which approaches roller 93 from cams 24. The actuation
clearance between roller 93 and cams 24 is therefore suppressed,
and engine brake openings of valves 4 and 5 can take place.
[0063] After the engine brake opening movements of valves 4 and 5
have been performed, piston 95 must be returned to its first
position. While check valve 97 remains closed, reset cam 26
cooperates with rolling surface 131 so that reset valve 99 rotates
around axis X99 towards its opened position represented on FIGS. 5
and 6, in order to let fluid flow in grooves 995 as previously
described. This fluid flow induces a pressure equalization between
main duct 103 and fluid inner chamber 113. As piston chamber 101
communicates with main duct 103, control fluid is allowed to flow
back from chamber 101 and fluid pressure is therefore reduced in
piston chamber 101.
[0064] In the phase during, which valves 4 and 5 return to their
closed position, under effect of the compression force of springs
41 and 51, a compression force F7 is transmitted to piston 95 via
valve bridge 7.
[0065] Opening of reset valve 99 is performed at a given time
during the closing movement of valves 4 and 5, so that piston 9
returns to its first position under action of compression force F7.
Piston 95 begins to return to its first position when force F7
becomes superior to the force exerted by fluid pressure in piston
chamber 101.
[0066] A second embodiment of the invention is represented on FIG.
7. In this embodiment, elements similar to the first embodiment
bear the same references and work in the same way. Particularly,
elements shown on FIGS. 2 to 6 are the same and work in the same
way in the embodiment of FIG. 7.
[0067] In this embodiment, rocker 9, via piston 95, exerts valve
opening force F9 only on a portion of valve bridge 7. This portion
is a slider block 71. Valve 4 is connected to slider block 71,
while valve 5 is connected to the remaining portion 72 of valve
bridge 7. Slider block 71 is movable with respect to bridge 7 along
opening axis X4 of valve 4. Consequently, valve 4 is also movable
with respect to valve bridge 7 along axis X4.
[0068] Rocker 9 further comprises a finger 121 substantially
parallel to piston 95, and located at a distance, with respect to
axis X91, superior to the distance between axis X95 and axis X91.
Piston 95 is arranged in rocker 9 so that it cooperates with slider
block 71, while finger 121 cooperates with the remaining portion 72
of valve bridge 7, by exerting a valve opening force F121. This
embodiment applies to the single valve brake technology, in which
only one valve is opened to realize the engine brake function. This
technology permits to reduce forces exerted on the valve actuation
mechanism, in order to improve the reliability of valve actuation
mechanism S and internal combustion engine 2 and/or to allow the
exhaust brake valve lifts to be performed at moments where the
pressure in the cylinder is higher.
[0069] In this embodiment, piston 95 acts on slider block 71 so as
to open valve 4. Normal exhaust openings of valves 4 and 5 are
implemented as follows. Piston 95 is first moved towards its second
position, so that, when the rotation of rocker 9 starts, opening of
valve 4 begins. When rotation of rocker 9 goes further, contact is
made between finger 121 and bridge portion 72. From this moment on,
valve bridge 7 is moved and opening of valve 5 begins.
[0070] At a further rotation angle of rocker 9, contact is lost
between piston 95 and slider block 91. From this moment on, bridge
portion 72 cooperates with slider block 71 thanks to a non-shown
stop which cooperates with a non-shown shoulder of slider block 71.
Slider block 71, and so on valve 4 become integral in translational
movement with bridge portion 72, until the opening of valves 4 and
5 completes.
[0071] To allow valves 4 and 5 to return to their closed position,
movements of bridge 7 are realized exactly in the opposite manner
as for the opening movement until contact is made again between
piston 95 and slider block 71. At this moment, as piston chamber
101 is closed, the elastic force of spring 41 is inferior to the
force exerted by fluid pressure on piston 95, and valve 4 therefore
closes at a smaller speed with respect to valve 5. This provokes
valve overlapping, which reduces the efficiency of the engine brake
function, because it can provoke admission of warm exhaust gases at
a wrong tune.
[0072] To reduce this valve crossing effect, reset valve 99 is
opened, thanks to reset cam 26, at the time when contact is made
between piston 95 and slider block 71, so that the elastic force
exerted by spring 41 on valve 4, and transmitted to slider block 71
overcomes the force of fluid pressure in piston chamber 101. This
allows to push back piston 95 towards its first position and to
insure valves 4 and 5 are substantially synchronized.
[0073] A third embodiment of the invention is represented on FIG.
8. This embodiment is described in combination with the embodiment
of FIGS. 1 to 6, in which two valves are moved by the valve
actuation mechanism, but may also be implemented with the
embodiment of FIG. 7, in which only one valve is moved.
[0074] In this embodiment, camshaft 2 does not comprise any
specific reset cam 26. Lever arm or cam follower 13 shows a
specific profile 133 which cooperates with cam 22 together with
roller or cam follower 93. Specific profile 133 forms a reset
profile which permits to obtain, under effect of rotation of cam
22, a movement of lever arm 13 which is partially independent from
the movement of rocker 9. Reset profile 133 comprises to this end
specifically formed cam sectors so as to obtain openings of reset
valve 99 at the times when piston 95 most be pushed back to its
first position.
[0075] According to a non-shown embodiment of the invention, valve
actuation mechanism S may apply to an engine having cylinders
equipped with a single exhaust valve and a single intake valve. In
this case, each rocker 9 is adapted to move only one valve, and the
valve opening actuator does not comprise any bridge, the single
exhaust or intake valve being moved via an intermediate part
adapted to cooperate with piston 95
[0076] According to a non-shown alternate embodiment, reset valve
99 may be of a non-rotative type.
[0077] In a further non-shown embodiment, the reset valve may be
designed to open a communication of the chamber 101 directly to the
exterior of the rocker, simply allowing oil a small quantity of oil
to escape out of the rocker in order to allow retraction of the
activation piston towards its first position.
[0078] In the above embodiments, the reset valve is distinct from
the check-valve 97. But, in still another embodiment, the reset
valve can be embodied as the check-valve itself, which would then
only be performing an additional function. For example, a mechanism
can be provided so that the reset profile causes the plunger 110 to
force the check valve 97 to its open position. Such mechanism would
act in parallel to spring 112, but would be able to overcome the
pressure in chamber 113 to force the plunger to its extended
position where it forces ball 109 off the seat.
* * * * *